Here's an ultra-fluffy (ie, G-rated, let along PG-13) way of dealing with the issue, if you need it:
Her sponsor, Death, is actually one side of a supernatural coin, with the other side being Life. Drawing too deeply from Death upsets the balance, resulting in her being compelled to serve Life in some way. In effect, the Debt points really reflect the balance that needs to be restored rather than an actual favor being done.
Another less fluffy option to add to the other suggestions:
* Compel her to "not intervene to change the fate" of someone she cares about who, without her help, would die.